Among materials which change in color when exposed to light is a photochromic substance. The photochromic substance has the property that its structure reversibly changes according to the presence or absence of ultraviolet radiation to change in absorption spectrum. This property results from the nature that when an isomer is irradiated with light of a particular wavelength, the single chemical substance, under the action of light, reversibly produces an isomer having a different absorption spectrum. The resulting different isomer is restored to the color of the original isomer by heat or light of a different wavelength.
Photochromic spectacles utilize the above nature of the photochromic material for lenses. In an outdoor environment exposed to light including ultraviolet radiation, such as sunlight, the lenses are rapidly colored to function as sunglasses. In an indoor environment without exposure to light, the lenses fade to function as ordinary transparent spectacles.
Known methods for producing a lens having photochromic property include a method of impregnating the surface of a non-photochromic lens with a photochromic coating fluid; a method dissolving a photochromic coating fluid in a monomer, and polymerizing the solution to obtain a photochromic lens directly; and a method providing a layer having photochromism on the surface of a lens with the use of a coating agent containing a photochromic compound.
In connection with the present invention, the technology of Japanese Unexamined Patent Publication No. 2000-334369 is available as an apparatus which can coat a plurality of lenses continuously, and the technology of Japanese Unexamined Patent Publication No. 2005-013873 is available as an apparatus equipped with an auxiliary mechanism for spreading a coating fluid on a lens with the use of a flexible film.
Of the above-described methods for producing a lens, the coating method, which coats a photochromic coating fluid, may carry out primer coating on the surface of a lens as pretreatment for a photochromic coating operation, in order to improve adhesion between a photochromic layer and a lens base material, and then perform photochromic coating.
In this primer coating operation, a primer coating fluid is ejected from the nozzle of a vessel or barrel containing the primer coating fluid to the surface of the lens, with the lens being rotated, to form a coating layer on the surface of the lens.
No problem is posed if lenses to be coated are same type which means size and gradient of lenses are identical, because the setting for the apparatus remains unchanged. However, if the coating fluid is to be applied to lenses different in size and gradient, it is necessary to adapt the apparatus to the shape of the lens. In this case, if the height or gradient of the lens is known beforehand, the setting of the apparatus can be adapted to their pattern. If the height or gradient of the lens is unknown, it is common practice to investigate the height or gradient of the lens anew, and then adjust the height of the lens or the height of the nozzle in accordance with a position suited to the lens, thereby rendering the coating layer uniform. In coating the lens, it is desired to coat many lenses in a short time with good efficiency.
The present invention has been accomplished in the light of such circumstances. It is an object of the invention to provide a coating apparatus which can detect the height and gradient of a lens automatically and easily, which forms a stable coating film, and which forms a coating film on each of many lenses in a short time.